The present invention relates generally to a liquid recovery system and method; and, more particularly, to a system and method for separating dissolved solid material from a liquid.
Pickling iron and steel to remove rust and scale is typically accomplished by using an aqueous sulfuric acid solution. The pickling process produces dissolved impurities, primarily ferrous sulfates, in the solution; and when the concentration of the dissolved impurities approaches a saturation level in the solution, the solution becomes ineffective and must be either disposed of or recovered by removal of the impurities.
Various processes are known for recovering spent pickling acid. Generally, these prior processes involve cooling the spent acid to cause the ferrous sulfate to crystallize out of the acid; and, thereafter, physically separating the precipitated crystals from the acid. Known processes include batch-type and continuous-type processes. In a batch-type process, a quantity of spent pickling acid is removed from a pickling tank and processed to separate the ferrous sulfate from the acid; and the recovered acid is then returned to the pickling tank for reuse. In a continuous-type process, spent pickling acid is withdrawn from the pickling tank in a continuous manner and caused to travel through an extended path along which the acid is gradually purified; and the recovered acid is then continuously returned to the pickling tank.
Neither batch-type nor continuous-type acid recovery processes known in the art are fully satisfactory. Batch-type processes often required interruption of a pickling operation while the spent acid was being recovered, and were generally not conducive to a high degree of automation. Continuous-type processes usually required large structures which occupied substantial space, and were generally not as effective as batch-type processes in removing substantially all impurities from the spent acid before it was returned to the pickling tank.
After being separated from the spent acid, the ferrous sulfate crystals are in the form of a thick, crystal slurry; and most acid recovery systems include structure for periodically removing the accumulated crystal slurry from the system. In most systems, the crystal removing structure comprised a rotating auger, basket or other movable component to push the crystal slurry out of the system, or pumping structure to pump the slurry out of the system.
Prior removing structures are also not fully satisfactory. For one thing, the slurry tends to adhere to internal surfaces of the system; and prior removing structures were often unable to fully remove the slurry. Also, prior removing structures often became clogged by the slurry and required frequent cleaning and maintenance for proper operation.